Examples of a state detecting device used for monitoring a state of the inside of a circuit in which a liquid flows are: a pressure measuring device detecting a pressure of the liquid flowing in the circuit according to a displacement of a diaphragm provided in a detecting device (see Patent Reference 1); and an optical detecting device detecting a turbidity of the liquid and concentration of specific components in the liquid according to light transmittancy.
When there are air bubbles in these detecting devices, the detecting devices fail to accurately detect the pressure or the light transmittancy. Therefore, it is necessary to remove air bubbles from the detecting devices.
Especially if these detecting devices are arranged in circuits, such as blood circuits, for taking blood from a body to be processed, accurate detection of a pressure or light transmittancy of a liquid flowing in the circuits is desired to provide crucial index for a human life.
The following describes the background art with reference to a blood circuit and a dialysis monitoring device as examples.
Hemodialysis is a treatment for flowing blood taken from a patient through a dialyzer that removes redundant water and waste products from the blood. A fluid channel connected to the patient is called a blood circuit. The blood taken from the patient by a blood pump provided in a dialysis monitoring device flows in the blood circuit, then is purified in the dialyzer connected to the blood circuit, and eventually returns to the body of the patient. A hollow fiber semipermeable membrane is provided in the dialyzer. The hollow fiber semipermeable membrane runs the blood in a hollow fiber and runs dialysate outside the hollow fiber, thereby transferring unnecessary products from the blood to the dialysate in order to remove the unnecessary products from the blood based on a principle of diffusion and filtration via the semipermeable membrane.
In general, the blood and the dialysate move in opposite directions (namely, they are countercurrent flow) so as to improve dialysis efficiency in treatments. Furthermore, the dialysate flows upwards outside the hollow fiber of the dialyzer. Therefore, the blood needs to flow downwards in the dialyzer to be countercurrent flow of the dialysate.
For preparation for the treatment, it is necessary to replace air in the blood circuit and the dialyzer by physiological saline solution or the like before flowing blood in the circuit.
In the preparation, processing of filling physiological saline solution or the like in the circuit using a blood pump of a dialysis monitoring device after setting the circuit in the dialysis monitor device is called “priming”. In the priming, a liquid flows downwards in a blood channel in the dialyzer where air is most likely to be left, thereby easily removing air from the circuit. More specifically, a liquid needs to flow downward in treatments and needs to flow upward in the priming. In short, the direction of flowing a liquid is opposite between the treatments and the priming. Therefore, in the priming, the dialyzer is turned over so that an inflow inlet of the dialyzer is positioned low and an outflow outlet of the dialyzer is positioned high, in order to perform preparation such as liquid exchange. In addition, when the priming is switched to the treatments, the dialyzer needs to be re-arranged to a correct direction, which requires considerably complicated processing when a plurality of dialysis patients are to be treated at the same time.    Patent Reference 1: Japanese Patent No. 3526965